Preparation of mixed tetraalkyl lead compounds



United States Patent US. 'Cl. 260-437 7 Claims ABSTRACT OF THEDISCLOSURE Tetraorganolead compounds containing at least two differentorganosubstituents are reacted in the presence of a silicontetrafluoride catalyst to produce mixed organolead compounds.

The instant invention is concerned with a method for producing mixedtetraorganolead compounds. More particularly, the invention relates to amethod for producing a mixture of tetraalkyl lead compounds with the useof a certain catalyst.

Recently, efforts have been made toward devising a simple, economicalmethod for producing a mixture of organolead compounds, which mixturewould find ready use as an antiknock additive. If such a mixture couldbe made whereby the many lead components would have varying boilingpoints, the composition mix would then be better suited for use as anantiknock ingredient for hydrocarbon fuels. These fuels are generally amixture of varying petroleum fractions having considerably differentboiling point ranges, which fractions in their entirety encompass arather broad boiling point range.

It would be desirable if a mixture of tetraorganolead compounds such astetraalkyl leads could be made either from a combination of lead alkyls,each having four identical alkyl groups, but with alkyl groups differingbetween two or more tetraalkyl leads, or from a single or moretetraalkyl lead compounds each one of which has two or more differentalkyl groups. Such a mixture itself would also have a broad boilingpoint range according to the number and type of lead components going tomake up the mixture. These lead components in turn would volatilize withthe various petroleum fractions, and thus impart excellent antikuockproperties to the petroleum hy drocarbon mixture, even though suchmixture contains a multitude of different hydrocarbon components whichvary widely in their volatilization properties. Improved performancecharacteristics therefore would 'be imparted by such a mixture oftetraalkyl lead compounds to all types of hydrocarbon mixtures which mayfind use in autos, diesels, and the like.

A further advantage would be realized if the components of thetetraalkyl lead mix could be predetermined by some method whereupon thelead alkyl mix composition could be tailor-made for a variety of fuelperformance requirements.

It would be an advance in the art if a mixture of alkyl lead compoundscould be produced by a simple, singlestep, inexpensive method. Otheradvantages would be gained if by such a method a lead mixture may beproduced within a relatively short period of reaction time, withoutresort to elevated temperatures. Yet such process should have at least aminimum reaction period so that it can be conveniently terminated at anytime to yield the desired proportion of mixed lead compounds.

U.S. Patent Nos. 3,151,141 and 3,151,142 describe methods for producinga mixture of tetraalkyl lead compounds. However, the processes describedtherein have certain drawbacks. For example, the disclosed use of3,441,582 Patented Apr. 29, 1969 "ice boron catalysts leads to asituation of a too rapid redistribution of alkyl lead reactants. Thisresults in a lack of sufficient time to properly follow the reaction byanalytical methods and quench the catalyst and reaction when the desiredlead mixture is reached. That is, the rapidity of the reaction does notallow one suflicient time to analyze aliquots of the process mix andcease reaction when the indicated proportion is reached. Following thepatented processes does not allow one of the desired time lag necessaryto carry out an analysis program.

It would be a step forward if a method could be discovered forrearranging lead alkyl radicals to produce a tetraalkyl lead compositethereof, through use of a catalyst system which is versatile enough toallow one sufficient time to follow the reaction and thus quench at thedesired point, but yet catalyzes the reaction rapidly enough to becommercially attractive. Further advantage would be realized if such acatalyst would have little or no susceptibility to product or reactantcontamination, and could be used in a variety of solvent systems.

Again, it would be a distinct advance in the art if a method ofproducing a tetraalkyl lead composite were known in which both thereaction rate and the final products of the mix could be controlled byvarying one or more process variants such as quantity of catalystemployed, time, and/or temperature. If a continuous method for producinga mixture of alkyl lead compounds were known, which process could beconveniently carried out at room temperature in a relatively short time,such a process would find ready acceptance, with the products thereofconstituting an excellent source of motor fuel antiknocking agent.

It, therefore, becomes an object of the invention to provide a methodfor producing a mixture of tetraorganolead compounds by a single step,efficient process which may be carried out at room or elevatedtemperatures Within a relatively short time.

Another object of the invention is to provide a method of producing atetraalkyl lead mixture, in which mixture, lead compounds are present inproportions tending to approach a theoretical equilibrium mixtureaccording to statistical laws of distribution which are stated in moredetail below.

A specific object of the invention is to provide a mixture of tetraalkyllead compounds which have for their radicals, methyl and ethyl groups,obtained by metathetical reactions which are catalyzed by a certaincatalytic material, which reaction may be carried out in a relativelyshort time even at room temperature, and yet has sufficient flexibilityso that the reaction may be stopped at any point short of theoreticalequilibrium.

In accordance with the invention, has has been found that a mixture oftetraorgano lead compounds such as tetraalkyl lead compounds may beproduced by rearranging a reaction mixture composed of one or more tetraorgano lead compounds containing at least two differentorganosubstituents in the presence of silicon tetrafluoride catalyst inorder to rearrange the organo constituents and produce a new mixture oflead compounds in proportions tending to approach a theoreticalequilibrium mixture. While discussion below of the process will bepresented in terms of tetraalkyl lead compounds for purpose ofsimplicity, it should be understood that the organo lead su-bstituentsmay Widely vary without departing from the scope of the invention.

The equilibrium mixture, or proportions of various compounds of themixture tending to approach this equilibrium, may be simply and easilysynthesized through a variety of starting materials. For example, asimple mixture may be made of two or more tetraalkyl lead compounds eachone of which compounds contain four identical organic radicals, but withradicals diifering in at least two occurrences between respective leadcom pounds. For example, a mixture of tetraethyl lead and tetramethyllead may be made and then the radicals rearranged by means of catalystat room temperature or at elevated temperatures. A metathetical reactiontakes place wherein a variety of diiferent compounds are produced havingvarying numbers of ethyl and methyl groups. These compounds are producedby rearrangement and/ or exchange of radicals of tetraethyl lead andtetramethyl lead. It is to be understood, of course, that a number oflead compounds may be mixed and redistributed with catalyst, with theonly requirement being that at least two diiferent alkyl radicals arepresent in order for the rearrangement and/or exchange to take place.Also, the reaction may be terminated at any point prior to completion byquenching the catalyst with a material such as water or any other polarsolvent. Thus, any desired combination of lead alkyl compounds may besimply made.

Another way of practicing the invention is to take a single tetraalkyllead compound which has at least two different alkyl groups substitutedthereon and contact this compound with the silicon tetrafluoridecatalyst in order to produce the theoretical number of compounds havingratios in such proportions as may be predicted by statistical laws ofdistribution, according to a theoretical calculation of the mixturewhich would be obtained at complete equilibrium. Again, two or moreheterogeneous tetraalkyl lead compounds may be employed, that is,compounds having at least two different alkyl lead radicals substitutedaround the lead atom. Likewise, one or more heterogeneous tetraalkyllead compounds may be combined with one or more homogeneous tetraalkyllead compounds, the latter being compounds having the four positionsaround the lead atom substituted with like radicals. These mixtures mayalso be rearranged by simple catalyst contact.

The radicals which may be rearranged on the lead substituents. Again,such lead compounds containing groups as phenyl, and substituted phenylmay also be employed in the rearrangement process of the invention.

If, one reacts, for example, one or more compounds in which there arepresent both methyl and ethyl radicals, there will be obtained ametathetical reaction which will eventually reach an equilibrium,dependent only upon the ratio of the number of methyl groups to thenumber of ethyl groups initially present, irrespective of the type ofcompound or compounds chosen as starting materials. If it is presumedthat the methyl ethyl lead compounds produced are thermodynamicallyequivalent, then a theoretical equilibrium distribution of methylethylleads corresponding to any starting ratio may be given by the terms ofthe binomial expansion (P+Q) where P is the mol fraction of methylgroups and Q=(1P) is the mol fraction of ethyl groups.

Table I below shows the theoretical mol ratios of various components ofa tetraalkyl lead mix composition which may be produced by varying themol fractions of the methyl and ethyl groups. The equilibrium mol ratioconcentrations, of course, are theoretical, and may not be exactlyreproduced by various experiments due to varying thermodynamic factors.However, mixtures having mol ratios extremely close to the theoreticalequilibrium distribution may be produced. Also, the metathetical radicalexchange reaction may be stopped at any point desired by theexperimenter, short of the theoretical equilibrium distribution. Notonly may the reaction be ten: minated short of equilibrium, to obtainvarying ratios of different lead alkyl compounds, but also the productsfrom the metathesis of starting mixtures of dissimilar compositions maybe also blended together to produce different mix compositions. Table Ibelow shows a number of typical theoretically attainable compositionsthat may be produced by equilibrating mixtures containing various molratios of tetraethyl lead to tetramethyl lead, and various mixtureswhich may be obtained by blending various quantities of equilibrates.

TABLE I.-TYPICAL THEORETICALLY ATTAINABLE COMPOSITIONS [M01 percent]EtiPb MeEtaPb MezEtgPb MeaEtPb MeiPb Remarks Range 0-100 042 0-38 0-420-100 1 6 25 38 25 6 Equilibrate equimolar mixtures of tetraethyl lead(TE L) and tetramethyl lead (TML).

2 41 41 15 3 0 Equilibrtate a mixture containing TEL, TML in a 4:1

m0 ta 0.

3 17 6 17 30 Equilibrate mixtures containing TEL and TML in 7.33:1 and1:7.33 mol ratios. Blend equal quantities of the equilibrates.

4 20 20 20 20 20 Equilibrate mixtures containing TEL and TML in a 2.45:1and 1:2.45 mol ratios. Blend equal quantities of the equilibrates withadditional TEL and TML. (Also nearly attainable by stopping short ofequilibrium with 1:1 ratios TML and TEL.

5 6 14 25 33 23 Equilibrate mixtures containing TEL and TML in 1:1

and 1:4 ratios. Blend equal quantities of the equilibrates.

atom may vary over a wide range of chemical constituents. To obtain highmobility of radical exchange between molecules it is preferred thatmaterials having lower alkyl radicals be employed as reactants. Suchmaterials may contain radicals as methyl, ethyl, isopropyl, npropyl,tetrabutyl, iso-butyl, n-butyl, etc. It is to be understood, of course,that higher alkyl radicals may also be rearranged through the method ofthe invention. However, in some of these cases involving the long chainradicals, in order to reach the desired mixture of compositions, it maybe necessary to contact the starting reactants with the catalystmaterial for longer periods of time than are necessary with the loweralkyl lead compounds. For simplicity of discussion, preparative examplesand general experimental techniques will be explained with regard toreaction between tetraethyl lead and tetramethyl lead. However, exactlyanalogous situations exist in cases of radical rearrangement with otherorgano 7 As mentioned above, the redistribution reaction eifected by thecatalyst may be extended over a wide range of times. For example,depending upon the type of mixture desired, or how close to theoreticalequilibrium the mix composition is desired, the tetraalkyl leadreactants may be rearranged for as short a time as /2 hour or as long as12 hours. Excellent conversion of reactants to various mixtures has beeneffected at from 1 to 6 hours. The average reaction time of the processof the invention is roughly ten times slower than a similar reactionutilizing boron trifluoride catalyst or derivatives, therefore leadingto advantages discussed above.

Again, depending upon the choice of the experimenter, the contact of thelead reactants may be carried out at room temperature or elevatedtemperatures. It has been determined that at elevated temperatures therate o f conversion is sometimes too rapid to allow one to cease thereaction at the desired point. Thus, effecting reaction at roomtemperature is preferred.

The redistribution of the lead alkyl compounds with the catalystmaterial may be carried out in a number of ways. In one method, thesilicon tetrafluoride gas is bubbled into a liquid batch of lead alkylreactant to initiate reaction. The reaction may be run in presence ofliquid scavengers as ethylene dibromide or ethylene dichloride or avariety of solvents as ethers without adversely 'afiecting the catalyst.Thus, the lead redistribution may be effected by first dissolving thelead reactants in any solvent which does not destroy the catalysteffectiveness and allowing the reaction to proceed to the extentdesired.

The amount of catalyst used may be varied over a considerable range.Again, the rate of reaction is dependent to a degree upon the amount ofcatalyst employed. Excellent results have been realized through use ofas little as 0.001% by weight of catalyst, based on the weight of leadreactant. Preferably, from 0.01 to 20% by weight of catalyst isemployed, with optimum results effected through use of from 0.01 to byweight of catalyst.

The reaction may be run in a variety of solvents or may also be carriedout without benefit of solvation. Any Organic solvent in which the leadcompounds are compatible may be used. Among these are benzene, ethers astetrahydrofuran, toluene, xylene, ethylene dichloride, carbontetrachloride and the like.

It has been discovered that the presence of water either in the catalystor as an impurity in the reactants severely retards the reaction andshould be avoided. However, water has been found to be an excellentquench medium to terminate redistribution.

Experimental runs indicated that there is substantially no change intotal alkyl lead concentrate, during the equilibration reaction. Thisindicates that there are no substantial side reactions taking place, andthe metathetical reaction, which most probably takes place through somesort of free radical exchange, is a clean reaction, causing no difiicultundesirable side effects.

Starting lead compounds may be made available by a number of knownprocedures. For example, the manufacture of organometallic compoundsand, more specifically, organic lead compounds by electrolyzing asolution of a Grignard reagent in an organic solvent for the Grignardreagent is disclosed in U.S. Patents 3,007,857 and 3,007,858. In theprocess disclosed in the latter patent, an extraneous organic halide isadded to the electrolyte.

A mixture of lead compounds can be made via the justcited patentedmethods by separately electrolyzing different Grignard reagents andequilibrating the products after mixture thereof. Again, a mixture ofalkyl lead compounds, such as triethylmethyl lead, diethyldimethyl lead,ethyltrimethyl lead, tetraethyl lead and tetramethyl lead may beproduced by using as an electrolyte an ether solution of mixtures ofmethyl magnesium halide such as the chloride and ethyl magnesium halide.After electrolysis, the mixture may then be equilibrated according tothe process of the invention by contact with catalyst with or withoutprior addition of lead compounds which may contain radicals other thanthe methyl or ethyl type. A variety of other Grignard reagents may alsobe electrolyzed singly or in admixture with one another. Specificexamples of these Grignard reagents are ethyl magnesium bromide,isopropyl magnesium bromide, isopropyl magnesium chloride, butylmagnesium chloride, butyl magnesium bromide, amyl magnesium bromide,amyl magnesium chloride and higher alkyl homologues. Similarly, phenylmagnesium chloride, phenyl magnesium bromide or mixtures of phenyl andethyl magnesium chloride, or mixtures of phenyl and ethyl magnesiumbromide, or mixtures of phenyl and methyl magnesium chloride, ormixtures of phenyl and methyl magnesium bromide can be electrolyzed toproduce a mixture of other organic compounds containing the phenylradical, or both the phenyl and ethyl radicals or both the phenyl andmethyl radicals, or both the phenyl and other alkyl radical in caseanother halide is substituted for the ethyl magnesium halide or themethyl magnesium halide. Similarly, benzyl magnesium chloride in anorganic ether can be employed alone or in mixture with one or more ofthe above-mentioned Grignard reagents or others to produce a suitableelectrolyte. Thus, if a mixture of the Grignard reagents is employed,the resultant mixed lead compounds may be equilibrated without additionof a further differing lead compound. If, on the other hand, a singleGrignard reagent is employed, at least one other diflfering organic leadcompound must be added prior to equilibration in order to achieve anequilibrated mix or one tending to approach a theoretical equilibriummixture.

The term Grignard reagent as used herein refers to the product obtainedby reacting approximately equimolar proportions of compounds having theformulae RX and Mg according to the equation:

in which R represents the organic radical, X represents the halogen atomof the Grignard reagent and Mg is the chemical symbol for magnesium. Asoutlined above, the radical R can be chosen from a Wide variety oforganic radicals, and as well, the radical X can be any halide, forexample, chloride, bromide or iodide.

The following example is given to more fully illustrate the invention.

EXAMPLE I A solution of 28.3% tetramethyl lead and 27.1% tetraethyl leadin a mixture of solvents of ethylene dibromide, ethylene dichloride andtoluene was prepared. Silicon tetrafiuoride catalyst was then bubbledinto the solution. At the completion of the run, a gas chromotographyanalysis indicated extensive equilibration had taken place. Analysis ofthe equilibrated mix yielded the following percentages of various leadcompounds present: tetramethyl lead, 8.7%; trimethylethyl lead, 12.3%;dimethyldiethyl lead, 17.7%; triethylmethyl lead, 14.0%; and tetraethyllead, 3.2%.

It has been demonstrated that any type of tetraalkyl lead mixcomposition may be obtained as desired by adjustment of any one of theseveral process variables or by ceasing the metathetical reaction priorto its theoretical equilibrium completion. The products of the inventionfind valuable use as antiknock motor fuel additives and, may be used fora variety of other uses involving organo metallics, or as syntheticorganic intermediates.

The invention is hereby claimed as follows:

1. A method of providing a mixture of tetraorganolead compounds, whichcomprises the step's of forming a reaction medium composed of at leastone tetraorganolead compound, said medium including at least twodifferent organoradicals, contacting said reaction medium with a silicontetrafluoride catalyst in order to rearrange said organoradicals andproduce a new mixture of organo lead compounds in proportions tending toapproach a theoretical equilibrium mixture.

2. The method of claim 1 wherein said reaction medium includes atetraalkyl lead compound.

3. A method of providing a mixture of lead alkyl compounds with at leastone component containing mixed alkyl radicals, which comprises the stepsof contacting at least one lead tetraalkyl compound having at least twodifferent alkyl radicals thereon with a silicon tetrafluoride catalystin order to rearrange said alkyl radicals to produce said new and usefulmixture of lead alkyl compounds.

4. A method of providing a mixture of lead tetraalkyl compounds with atleast one component containing mixed alkyl radicals, which comprises thesteps of contacting at least two lead tetraalkyl compounds, eachcompound containing four identical organic radicals, but with organicradicals differing between at least two compounds, with a silicontetrafiuoride catalyst in order to rearrange said alkyl radicals toproduce said new and useful mixture of lead alkyl compounds.

5. The method of claim 3 wherein said radicals are selected from thegroup consisting of methyl and ethyl.

6. The method of claim 4 wherein said radicals are selected from thegroup consisting of methyl and ethyl.

7. The method of claim 1 wherein said rearrangement reaction isterminated prior to reaching equilibrium by quenching catalyst activityby contact thereof with water.

References Cited UNITED STATES PATENTS TOBIAS E. LEVOW, PrimaryExaminer. 10 H. M. S. SNEED, Assistant Examiner.

US. Cl. X.R.

